Numerous packaging bags and numerous systems for manufacturing them have already been proposed.
For bags of small thickness, that is, those that are generally flat in the filled state, known means generally provide satisfaction. Under such circumstances, the bags are generally formed using two planar sheets that are bonded together along three sides and that are provided with closure means, to example, complementary male/female strips, at the mouth of a bag.
In contrast, until now, manufacturing bags that are intended to receive contents that are thick, has turned out not to be entirely satisfactory, even though a large amount of research has been performed in this very specific field.
In particular, such bags often require lateral bellows which are difficult to make.
Accompanying FIG. 1 shows, diagrammatically, a known technique for manufacturing bags with lateral bellows by inserting pre-formed bellows 10 between two sheets 12 and 14 that constitute two main faces of the bags, with the bellows being inserted at 90.degree. to the travel direction S of the sheets 12, 14. The sheets 12 and 14 are provided with longitudinal male/female closure strips 13 and 15. The bellows 10 are preferably of varying width, increasing away from the closure strips 13 and 15 so as to enable the bags to be inflated. That known technique does indeed manufacture it possible to make packaging bags having lateral bellows. Nevertheless, it turns out to be quite complex. In particular, the need to insert the bellows 10 at 90.degree. to the travel direction of the sheets 12 and 14 does not enable high manufacturing throughputs to be obtained, and requires insertion of the bellows 10 to be adequately synchronized with the travel of the sheets 12 and 14.
Document FR-A-2 686 063 describes another technique of manufacturing packaging bags with bellows that consists in preforming a bag with lateral bellows, in splitting the bag over a portion of its length along fold lines external to the bellows, in folding the flaps defined in this way back over the outside of the bag, in placing the closure strips on the flaps, in reforming the bag, and in bonding the closure strips to the flaps that have been put into place. Unfortunately, because of its complexity, that technique does not provide full satisfaction.
The Applicant has also described various alternative solutions for manufacturing packaging bags with lateral bellows in French patent application No. 96 02389 filed on Feb. 27, 1996.